☣️ UN 1638 • CLASS 6
Mercury iodide
Placard: Toxic. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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Quick details
UN 1638
Class: 6
Placard type: Toxic
ERG: Guide 151 (check current ERG)
Isolation: ERG 151: isolate spill/leak area 25m in all directions; for large spills isolate 50m and consider evacuation; if fire involves material, isolate 800m in all directions
Chemical & Response Details
| Also known as | Mercuric iodideMercury(II) iodideRed mercury iodideHgI2Biniodide of mercury |
| CAS Number | 7774-29-0 |
| Appearance | Odorless red to yellow crystalline powder or solid. Scarlet red crystals are the most common form at room temperature. |
| Flash Point | Not applicable (non-combustible solid) |
| Boiling Point | 354C (669F) with decomposition |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Insoluble in water; no significant reaction |
| Extinguishing | Dry chemical, CO2, or dry sand appropriate for surrounding fire; material itself does not burn |
| PPE | ⚠️ Level B minimum with SCBA; full chemical-resistant suit required to prevent skin contact; highly toxic by all routes of exposure |
| Isolation | ERG 151: isolate spill/leak area 25m in all directions; for large spills isolate 50m and consider evacuation; if fire involves material, isolate 800m in all directions |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- Highly toxic, may be fatal if inhaled, ingested or absorbed through skin.
- Avoid any skin contact.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental
- Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive
- Containers may explode when heated.
- Runoff may pollute waterways.
First actions (field-minded)
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
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UN 1638 — Mercury iodide HAZMAT RADIO NOTE — UN 1638
Product: Mercury iodide
Class 6 / Toxic / ERG 151
PPE: Level B minimum with SCBA; full chemical-resistant suit required to prevent skin contact; highly toxic by all routes of exposure
ISOLATION: ERG 151: isolate spill/leak area 25m in all directions; for large spills isolate 50m and consider evacuation; if fire involves material, isolate 800m in all directions
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 1638 — Mercury iodide
Class: 6 | Placard: Toxic | ERG Guide: 151
Appearance: Odorless red to yellow crystalline powder or solid. Scarlet red crystals are the most common form at room temperature.
Water Reactivity: Insoluble in water; no significant reaction
Extinguishing: Dry chemical, CO2, or dry sand appropriate for surrounding fire; material itself does not burn
PPE: Level B minimum with SCBA; full chemical-resistant suit required to prevent skin contact; highly toxic by all routes of exposure
Isolation: ERG 151: isolate spill/leak area 25m in all directions; for large spills isolate 50m and consider evacuation; if fire involves material, isolate 800m in all directions
— Key Hazards —
• Highly toxic, may be fatal if inhaled, ingested or absorbed through skin.
• Avoid any skin contact.
• Fire may produce irritating, corrosive and/or toxic gases.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
SOURCE: allfirefighter.com/hazmat/un/1638 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN1638 Mercury iodide Cls6 ERG151 | ERG 151: isolate spill/leak area 25m in all directions; for large spills isolate | allfirefighter.com/hazmat/un/1638SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions. Page: https://allfirefighter.com/hazmat/un/1638
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FAQ
Highly toxic, may be fatal if inhaled, ingested or absorbed through skin. Avoid any skin contact. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive Containers may explode when heated. Runoff may pollute waterways.
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level B minimum with SCBA; full chemical-resistant suit required to prevent skin contact; highly toxic by all routes of exposure
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 151 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles. This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.